1. Field of the Invention
The present invention relates to an automatic control device for a motorized vehicle gearbox.
2. Description of the Related Art
A typical two-wheeled motorized vehicle cannot move backwards. Nevertheless, a beach motorcycle must have this function to avoid getting stuck when desired.
FIG. 15 of the drawings illustrates a conventional motorized vehicle gearbox with a control mechanism for controlling forward/backward movement. FIG. 16 is a perspective view of main parts of the gearbox in FIG. 15. The gearbox includes a transmission shaft 4′, a first gear 1′ mounted on the transmission shaft 4′ via a bearing 11′ for forward driving, a second gear 2′ mounted on the transmission shaft 4′ via a bearing 21′ for rearward driving, a first follower shaft 6′, and a second follower shaft 7′. A movable block 3′ is mounted on the transmission shaft 4′ to move therewith. Further, the movable block 3′ is slidable along a longitudinal direction of the transmission shaft 4′. The movable block 3′ includes two protrusions 31′ respectively on two sides thereof for respectively and releasably engaging with one of an engaging groove 12′ defined in a side of the first gear 1′ and an engaging groove 22′ defined in a side of the second gear 2′. The movable block 3′ is connected to an actuating rod 5′ to move therewith.
When the actuating rod 5′ is shifted to move the movable block 3′ to a position in which one of the protrusions 31′ is engaged in the engaging groove 12′ of the first gear 1′ or the engaging groove 22′ of the second gear 2′, one of  the first shaft 6′ and the second shaft 7′ is turned, thereby driving the motorized vehicle forward or backward. However, operation of the actuating rod 5′ is required.
FIG. 17 of the drawings illustrates a motorized vehicle gearbox with another conventional control mechanism for controlling forward/backward movement. FIG. 18 is a perspective view of main parts of the gearbox in FIG. 17. To solve the inconvenience of operation of the actuating rod, the control mechanism in FIG. 17 comprises an automatic control device 8′ including a motor 81′, a reduction gear 82′, and a screw 83′ that meshes with the actuating rod 50′. Thus, the motor 81′ can be activated to move the actuating rod 50′ via transmission by the reduction gear 82′ and the screw 83′. Nevertheless, the motor 81′ must be activated to turn in a reverse direction for moving the actuating rod 50′ in a reverse direction, which causes inconvenient control movement. Further, the travel “X” (FIG. 17) of the first gear 1′ to the second gear 2′ (or vice versa) is fixed, yet the travel of the actuating rod 50′ on the screw 83′ is not fixed. As a result, the movable block 3′ might impinge the first gear 1′ and/or the second gear 2′.
Further, the protrusion 31′ of the movable block 3′ may not be exactly aligned with, e.g., the engaging groove 12′ of the first gear 1′ (FIG. 18) during rotation of the movable block 3′. Namely, the movable block 3′ has to turn through a small angle to allow insertion of the protrusion 31′ into the engaging groove 12′. Transmission of the control device is not reliable. Further, damage to the parts of the control mechanism resulting from impingement occurs, as no buffering means is provided. 